This invention relates to metal substrates containing a ceramic coating, and is particularly directed to metal substrates such as titanium, containing an electrodeposited coating of a ceramic material, especially hydroxylapatite or similar calcium phosphate material, and cobalt, and having particular applicability as medical surgical implants.
The medical profession has been trying to develop a successful long term human implant for many years, and has yet to develop one that will last for 7 to 10 years in high stressed locations, e.g. hip prostheses and dental implants. The short service time before failure is of special concern in the case of younger patients as additional surgical operations are necessary.
Numerous techniques have been tried but none have been proven successful due to the loss of structural bonding between the human tissues and the metal substrate (implant). Loosening of the implant in the surrounding bone, leads to pain, and requires surgical removal in replacement of the device. Also, adverse tissue reaction is a problem due to the exposed metallic surface, which in time will corrode and release metallic ions which cause damage to the surrounding tissue.
Metal substrates such as titanium alloys have heretofore been coated with hydroxylapatite by various processes such as plasma spraying, ion sputter deposition and electrophoretic deposition in an attempt to obtain chemical bonding to the bone surrounding the implant, thus stabilizing the device.
A primary drawback of all such ceramic coatings has been the lack of strength of the bond between the ceramic, e.g. hydroxylapatite, material and the metal substrate. Further, each of the coatings produced by the above processes has proven unsatisfactory for various reasons such as low bond strength, variation in density, lack of crystallinity, low durability and high cost.
U.S. Pat. No. 3,945,893 to Ishimori et al discloses forming a low-abrasion surface on a metal base member by dispersing fine particles of a hard material in a metal plating solution, immersing in such solution a metal object to be coated as a cathode together with a metal rod as an anode, and passing current through the bath to codeposit a coating of the anode metal and fine particles of the hard material on the metal base member. According to a preferred embodiment, powdered silicon carbide is dispersed in a nickel plating solution such as a nickel sulfamate bath, and an aluminum alloy base member is immersed as a cathode in the bath and a nickel rod as an anode. A current is passed through the bath and a plated coating of nickel and silicon carbide is formed on the aluminum alloy base member. The metal deposit thus formed on the base metal surface is then subjected to polishing to remove a given thickness of the metal coating, leaving the hard fine particles partly exposed and protruded from the deposited layer.
One object of the present invention is to provide both smooth and porous surfaced metal substrates with ceramic coatings, particularly a calcium phosphate coating, so that the resulting ceramic coated substrates have good bond strength and the coating is uniform and durable.
Another object of the invention is the provision of metal substrates such as titanium and its alloys, containing a coating including hydroxylapatite as ceramic material, and a metal, and having characteristics suitable for use as medical implants, including hip prostheses and dental endosseous subperiosteal implants, permitting human tissues to attach and grow onto the coating and insure a strong structural bond between the human tissue and the ceramic coating, free from adverse tissue reaction, and such that the implant will be durable and have an indefinite life.
Still another object is to provide ceramic coated substrates of the above type, wherein the ceramic, particularly hydroxylapatite, is co-deposited with a metal on the substrate, e.g. titanium substrate, to aid in holding the ceramic to the metal.
Yet another object is the provision of a procedure for depositing a coating containing a calcium phosphate ceramic material, e.g. hydroxylapatite, on the substrate.
A still further object is to provide a process for co-depositing the ceramic material, particularly hydroxylapatite, and a metal, particularly cobalt, on the metal substrate.